*{
    padding: 0;
    margin: 0;
}
body{
    display: flex;
    justify-content: center;
    align-items: center;
    /* 让页面占屏幕总高 */
    height: 100vh;
    background-color: #000;
}
a{
    position: relative;
    width: 400px;
    height: 100px;
    line-height: 100px;
    text-align: center;
    text-decoration: none;
    /* 控制文本大小  仅英文*/
    text-transform: uppercase;
    color: #fff;
    font-size: 24px;
    border-radius: 50px;

    background-image: linear-gradient(to right,
    #03a9f4,#f441a5,#ffeb3b,#09a8f4);
  background-size: 400%;

 

}
a:hover{
    animation: sun 8s infinite;
}
a::before{
content: '';
position: absolute;
top: -5px;
bottom: -5px;
left: -5px;
right: -5px;
border-radius: 50px;
/* 背景渐变 */
background-image: linear-gradient(to right,
#03a9f4,#f441a5,#ffeb3b,#09a8f4);
background-size: 400%;
z-index: -1;
/* 模糊程度 */
filter: blur(20px);
}
a:hover::before{
    animation: sun 8s infinite; 
}
@keyframes sun {
100%{
    background-position: -400% 0;
}
}